It is often necessary to remove small, weakly magnetic grains of impurity from fibrous material, such as in the preparation of asbestos for use in high temperature electrical insulation and in the preparation of special tissue paper for use as a dielectric insulator in electric capacitors. The removal of impurity grains must be virtually complete because, for example, even a single grain in the hundreds of square meters of capacitor tissue used in a capacitor may make the product unacceptable. The removal of grains from fibrous media is extremely difficult. The fibers tend to envelop and trap the grains and the fibers are very prone to clogging. Fibrous fluids are usually pumped through highly polished ducts and fittings for any sharp protrusion would disrupt the streamlined flow causing "strapling" of the fibers: bending of the fibers over the obstruction. These characteristics of fibers and fiber separation marshall against the use of conventional high gradient magnetic separators, presently the most effective means for removing small, weakly magnetic particles, for such separators rely on a matrix of finely divided ferro-magnetic filamentary materials such as steel wool, mesh, or expanded metal which easily become clogged by the fibers. The more conventional, less effective magnetic separators do not appear to be adequate for this task. Typically present techniques for liberating granular impurities require that fibrous pulp must be handled in extremely dilute form typically 1% to 2.5% by weight in the case of asbestos and even more dilute in the case of capacitor tissue. In the opinion of some there is no wholly satisfactory method of separation for use in the preparation of capacitor tissue. In the preparation of insulating asbestos, where purity requirements may be much lower, there is a rather complex process being used, see U.S. Pat. No. 3,372,803. In this process the fiber pulp in the form of a 1% to 2.5% slurry is first passed at high velocity through several stages of cyclone in order to remove the largest of the impurity grains by centrifugal force. Next the slurry is passed through a solenoid magnet where it is subjected to a strong magnetic field which serves to magnetize particles that are capable of retaining magnetization (often referred to as magnetically "hard") so that they substantially coagulate into larger particles. Magnetically "soft" particles do not remain magnetized and therefore cannot be flocculated by a single pass through a magnet at high flow velocity. This process is mostly effective for magnetite grains and not so effective for material such as iron, hematite, and various other oxides. Subsequently the slurry is pumped through a smooth pipe into which protrude a plurality of poles of electromagnets which are designed to prevent "strapling" of the fibers while at the same time producing regions of low flow velocity such as eddies where granular particles of adequate size can be trapped.